Showerhead and method for manufacturing the same

ABSTRACT

A showerhead provided in a chamber of a semiconductor manufacturing apparatus and facing a wafer holder includes: a disk-shaped member having a plurality of through holes penetrating the disk-shaped member in a direction of a thickness thereof; a high-frequency conductor embedded in the disk-shaped member; a hole provided in the disk-shaped member, extending in the direction of the thickness of the disk-shaped member and having a bottom exposing a portion of the conductor; an electrode terminal portion disposed in the hole and having a base portion electrically connected to the conductor and a columnar portion provided on the base portion; a cylindrical member having a first end portion fitted outside the columnar portion and facing the conductor and a second end portion facing away from the first end portion, and a sealing member surrounding the first end portion.

TECHNICAL FIELD

The present disclosure relates to a showerhead and a method formanufacturing the same. The present application claims priority based onJapanese Patent Application No. 2017-146192 filed on Jul. 28, 2017, andincorporates herein all the contents described in the Japanese PatentApplication.

BACKGROUND ART

In semiconductor manufacturing apparatuses for manufacturingsemiconductor devices such as LSIs, a semiconductor wafer is placed on awafer holder, also referred to as a susceptor, introduced in a chamber,and, while having a back surface heated, has a front surface subjectedto a variety of types of thin film processing such as CVD, sputteringand other deposition processes, etching, and the like. Such thin filmprocessing may be performed in a plasma atmosphere, and a semiconductormanufacturing apparatus used in that case is provided with radiofrequency (RF) electrodes, with one (or a lower) electrode embedded inthe wafer holder and the other (or an upper) electrode above the waferholder to face the lower electrode. By applying radio frequency (RF)voltage between the electrodes, a source gas present between theelectrodes can be made into a plasma state.

In the chamber of the above semiconductor manufacturing apparatus, ashowerhead is provided above the wafer holder in order to introduce thesource gas. The showerhead generally has a portion facing a wafercarrying surface of the wafer holder and having a disk-shaped memberprovided with a large number of gas discharging holes so that the sourcegas can be uniformly supplied toward the wafer carrying surface of thewafer holder. Embedding a conductive member in the disk-shaped memberfor a radio frequency electrode allows the showerhead to also serve asthe upper electrode. For example, PTL 1 discloses that an upperelectrode circuit for generating a radio frequency wave is embedded in aceramic plate for a showerhead having a plurality of gas dischargingholes and a metal support holding the ceramic plate and the upperelectrode circuit are electrically connected by using a spring.

CITATION LIST Patent Literature

PTL1: Japanese Patent Laying-Open No. 2008-294017

SUMMARY OF INVENTION

A showerhead of the present disclosure is a showerhead provided in achamber of a semiconductor manufacturing apparatus and facing a waferholder, and includes: a disk-shaped member having a plurality of throughholes penetrating the disk-shaped member in a direction of a thicknessthereof; a high-frequency conductor embedded in the disk-shaped member;a hole provided in the disk-shaped member, extending in the direction ofthe thickness of the disk-shaped member and having a bottom exposing aportion of the conductor; an electrode terminal portion disposed in thehole and having a base portion electrically connected to the conductorand a columnar portion provided on the base portion; a cylindricalmember having a first end portion fitted outside the columnar portionand facing the conductor and a second end portion facing away from thefirst end portion, the second end portion's outer diameter being smallerthan the first end portion's outer diameter, the second end portion'sinner diameter being larger than the first end portion's inner diameter;and a sealing member surrounding the first end portion.

According to the present disclosure, a method for manufacturing ashowerhead comprises: forming a hole in a disk-shaped member, which hasa high-frequency conductor embedded therein, in a direction of athickness of the disk-shaped member to expose a portion of theconductor; connecting an electrode terminal portion to the conductorexposed at a bottom of the hole; fitting a glass preform in a form of adoughnut to the electrode terminal portion; fitting to the electrodeterminal portion a cylindrical member having a first end portion facingthe conductor and a second end portion facing away from the first endportion, the second end portion's outer diameter being smaller than thefirst end portion's outer diameter, the second end portion's innerdiameter being larger than the first end portion's inner diameter;fusing the glass preform; pressing the cylindrical member toward theconductor until the fused glass preform protrudes into a gap between thediameter-reduced portion and an inner wall of the hole and a gap betweenthe diameter-increased portion and an outer peripheral surface of theelectrode terminal portion; and solidifying the fused glass preform toseal the cylindrical member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic plan view of a showerhead according to anembodiment.

FIG. 1B is a cross section taken along a line 1B-1B indicated in FIG.1A.

FIG. 2 is a partial cross section of a first specific example of ashowered according to an embodiment.

FIG. 3A is a partial cross section of a second specific example of ashowered according to an embodiment.

FIG. 3B is a partial cross section of a third specific example of ashowered according to an embodiment.

FIG. 4A is a partial cross section of a fourth specific example of ashowered according to an embodiment.

FIG. 4B is a partial cross section of a fifth specific example of ashowered according to an embodiment.

FIG. 5 is a schematic perspective view of a cylindrical member.

FIG. 6 is a schematic cross section of a semiconductor manufacturingapparatus.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

As has been set forth above, when the upper electrode is embedded in thedisk-shaped member of the showerhead, the disk-shaped member is providedwith a hole in a surface thereof facing away from a surface thereoffacing the wafer holder and an electrode terminal portion is connectedto the upper electrode exposed at the bottom of the hole to feed theupper electrode with power. However, the chamber has an internalatmosphere in a corrosive environment, and a connection portion betweenthe upper electrode and the electrode terminal portion may provide poorconnection due to corrosion.

The present disclosure has been made in view of such a conventionalsituation, and contemplates a showerhead having a sealing structure inwhich an electrical connection portion between a conductor such as anupper electrode embedded in a disk-shaped member of the showerhead andan electrode terminal portion for feeding the conductor with power isless likely to provide poor connection.

Advantageous Effect of the Present Disclosure

According to the present disclosure, poor connection of the electricalconnection portion between the upper electrode and the electrodeterminal portion for feeding the upper electrode with power is lesslikely to occur.

Initially, embodiments of the present disclosure will be enumerated andspecifically described. A showerhead according to an embodiment is ashowerhead provided in a chamber of a semiconductor manufacturingapparatus and facing a wafer holder, and includes: a disk-shaped memberhaving a plurality of through holes penetrating the disk-shaped memberin a direction of a thickness thereof; a high-frequency conductorembedded in the disk-shaped member; a hole provided in the disk-shapedmember, extending in the direction of the thickness of the disk-shapedmember and having a bottom exposing a portion of the conductor; anelectrode terminal portion disposed in the hole and having a baseportion electrically connected to the conductor and a columnar portionprovided on the base portion; a cylindrical member having a first endportion fitted outside the columnar portion and facing the conductor anda second end portion facing away from the first end portion, the secondend portion's outer diameter being smaller than the first end portion'souter diameter, the second end portion's inner diameter being largerthan the first end portion's inner diameter; and a sealing membersurrounding the first end portion. Thus, poor connection of theelectrical connection portion between the upper electrode and a terminalportion for feeding the upper electrode with power is less likely tooccur.

In the above embodiment, the showerhead may further have a connectionportion that is disposed in the hole and electrically connects theconductor and the base portion. Furthermore, the base portion may have aflange portion facing the conductor. A larger electrical connectionportion can be obtained and in addition, the electrode terminal portioncan be more firmly fixed.

Furthermore, the cylindrical member may cover at least a portion of anupper surface of the flange portion by the first end portion. As aresult, the electrode terminal portion can be more reliably fixed, andan electrical connection portion between the conductor and the electrodeterminal portion can be more reliably sealed. Furthermore, theconnection portion may include a conductive annular member and mayinclude a conductive member in the form of a hollowed conical frustumincreased in diameter in a direction from the conductor toward the baseportion. This allows more reliable electrical connection.

Furthermore, in the above embodiment, the sealing member may fill a gapformed between the cylindrical member and the electrode terminal portionand a gap formed between the cylindrical member and the hole. Reliablesealing can be provided on a side radially inner than the cylindricalmember and a side radially outer than the cylindrical member and inaddition, on the side radially outer than the cylindrical member, aplane parallel to the direction of the thickness of the gas dischargingportion and a plane perpendicular to the direction of the thickness ofthe gas discharging portion can both be sealed, and sealability can thusbe enhanced. Furthermore, the cylindrical member may be made of aluminumnitride, and the sealing member may be made of glass. This can furtherenhance the corrosion resistance of the connection portion between theconductor and the electrode terminal portion.

According to an embodiment, a method for manufacturing a showerheadcomprises: forming a hole in a disk-shaped member, which has ahigh-frequency conductor embedded therein, in a direction of a thicknessof the disk-shaped member to expose a portion of the conductor;connecting an electrode terminal portion to the conductor exposed at abottom of the hole; fitting a glass preform in a form of a doughnut tothe electrode terminal portion; fitting to the electrode terminalportion a cylindrical member having a first end portion facing theconductor and a second end portion facing away from the first endportion, the second end portion's outer diameter being smaller than thefirst end portion's outer diameter, the second end portion's innerdiameter being larger than the first end portion's inner diameter;fusing the glass preform; pressing the cylindrical member toward theconductor until the fused glass preform protrudes into a gap between thediameter-reduced portion and an inner wall of the hole and a gap betweenthe diameter-increased portion and an outer peripheral surface of theelectrode terminal portion; and solidifying the fused glass preform toseal the cylindrical member. This can stably seal the electricalconnection portion between the upper electrode and the electrodeterminal portion for feeding the upper electrode with power.

Hereinafter reference will be made to the drawings to describe anembodiment of a showerhead according to the present disclosure. Withreference to FIG. 6, a showerhead 4 is provided in a chamber 3, in whicha semiconductor wafer 2 to be processed is subjected to thin filmprocessing such as plasma CVD in a plasma atmosphere, above a waferholder 8 holding and heating semiconductor wafer 2. As shown in FIGS. 1Aand 1B, showerhead 4 has a disk-shaped member 10 serving as a gasdischarging portion having a thickness of about 3.0 to 10.0 mm and anouter diameter of about 300 to 400 mm. Showerhead 4 has at an endthereof facing wafer holder 8 a gas discharging portion having gasdischarging holes 10 a which are a plurality of through holes providedthrough disk-shaped member 10. With reference to FIGS. 1A and 1B,showerhead 4 has disk-shaped member 10 having a thickness of about 3.0to 10.0 mm and an outer diameter of about 300 to 400 mm for discharginga gas as a source for a plasma toward wafer holder 8. Disk-shaped member10 has a plurality of gas discharging holes 10 a having an innerdiameter of about 0.1 to 5.0 mm. The plurality of gas discharging holes10 a are provided in a concentric, radial or similar pattern forexample.

Showerhead 4 is provided so as to face a wafer carrying surface 9 ofwafer holder 8 in parallel. This allows a plasma generating source gasto be supplied uniformly toward wafer carrying surface 9. Disk-shapedmember 10 is formed of a ceramic material such as aluminum nitride,silicon nitride, silicon carbide, aluminum oxide, and so forth to ensureelectrical insulation for a conductor 11, as will be describedhereinafter. Inter alia, aluminum nitride is preferable as it has highthermal conductivity and also has excellent corrosion resistance.

Inside disk-shaped member 10, conductor 11 for the upper electrode isembedded for example in the form of a generally circular thin film.Conductor 11 may be formed of any material insofar as it is electricallyconductive. The conductor may be formed for example of metal foil suchas stainless steel foil or by screen-printing and firing a pastecontaining tungsten or similar metal powder. Disk-shaped member 10 hasgas discharging holes 10 a penetrating disk-shaped member 10 in thedirection of the thickness thereof, and accordingly, conductor 11 isprovided with an opening at a position corresponding to each gasdischarging hole 10 a.

Referring to FIG. 2, in order to feed conductor 11 with power, one ormore circular holes 10 b having an inner diameter of about 5 to 20 mmare provided in a peripheral portion of disk-shaped member 10. Anelectrode terminal portion 12 having an outer diameter of about 1.5 to10 mm is connected to conductor 11 partially exposed from the bottom ofhole 10 b. By connecting a lead wire (not shown) that is connected toelectrode terminal portion 12 to an output terminal (not shown) of apower supply, conductor 11 can be fed with power. Electrode terminalportion 12 is provided at the peripheral portion of disk-shaped member10 because electrode terminal portion 12 provided at a central portionof disk-shaped member 10 would prevent that portion from having gasdischarging hole 10 a and hence prevent a gas from being uniformlydischarged.

A specific example of a structure of the connection portion betweenconductor 11 and electrode terminal portion 12 will be described indetail with reference to FIG. 2. Hole 10 b that is circular in a planview is provided in disk-shaped member 10 at a surface facing away fromthat facing wafer holder 8. Hole 10 b has a depth that reaches conductor11. Therefore, conductor 11 is partially exposed from the bottom of hole10 b. For example, electrode terminal portion 12 made of tungsten isdirectly connected to the exposed portion.

Electrode terminal portion 12 may have a general, substantially columnarshape. However, in a first specific example shown in FIG. 2, a baseportion 12 b is provided at an end portion on a side connected toconductor 11. A columnar portion 12 c is provided on base portion 12 b.A flange portion 12 a surrounds base portion 12 b. Base portion 12 b andflange portion 12 a have a lower surface directly connected to conductor11. This ensures a larger area for electrical connection with conductor11.

Instead of the structure in which base portion 12 b and flange portion12 a are directly connected to conductor 11, a second specific exampleis shown in FIG. 3A. In this example, an annular member 14 made forexample of tungsten and having an outer diameter substantially equal tothat of flange portion 12 a is used to connect to conductor 11. Aplate-shaped member 13 is disposed inside annular member 14.Plate-shaped member 13 is preferably made of the same material asdisk-shaped member 10, i.e., ceramic. Plate-shaped member 13 and annularmember 14 constitute connection portion 20. Annular member 14 can beformed for example by printing and firing a paste containing tungsten orsimilar metal powder on the outer peripheral surface of plate-shapedmember 13. Annular member 14 may be a member of metal such as tungstenformed in an annular shape in advance.

A third specific example is shown in FIG. 3B. In this example, a member114 of tungsten in the form of a hollowed conical frustum having atapered structure having a diameter gradually decreased as it approachesconductor 11 is used to connect to conductor 11. Inside member 114 inthe form of the hollowed conical frustum is disposed a truncated conicalmember 113. Member 114 in the form of the hollowed conical frustum ispreferably made of the same material as disk-shaped member 10, i.e.,ceramic. Truncated conical member 113 and member 114 in the form of thehollowed conical frustum constitute connection portion 200. Member 114in the form of the hollowed conical frustum can be formed for example byprinting and firing a paste containing tungsten or similar metal powderon the outer peripheral surface of truncated conical member 113. Member114 in the form of the hollowed conical frustum may be a member of metalsuch as tungsten formed in a hollowed shape in advance. Theconfiguration shown in FIG. 3A or 3B more reliably provide electricalconnection.

A fourth specific example is shown in FIG. 4A. Referring to FIG. 4A,electrode terminal portion 112 made of tungsten has a base portion 112 cand a columnar portion 112 d provided on base portion 112 c. Further,base portion 112 c is provided with a flange portion 112 a. Further, amale screw portion 112 b is provided on a side closer to a tip thanflange portion 112 a. Further, disk-shaped member 10 is provided with afemale screw portion 10 c. Male screw portion 112 b and female screwportion 10 c may be screwed together. This can more reliably fixelectrode terminal portion 112. Thus, when providing male screw portion112 b, a tip of male screw portion 112 b may directly be connected toconductor 11, as shown to FIG. 4A. In a fifth specific example shown inFIG. 4B, conductor 11 may be provided with a through hole for male screwportion 112 b so that an outer peripheral portion of flange portion 112a and a portion of conductor 11 surrounding the throughhole may bedirectly connected together.

Referring to FIGS. 2 to 5, a cylindrical member 15 having an innerdiameter larger than an outer diameter of electrode terminal portions 12and 112 by about 0.05 to 0.20 mm and an outer diameter smaller than aninner diameter of hole 10 b by about 0.05 to 0.20 mm is fitted toelectrode terminal portions 12 and 112. Cylindrical member 15 issuitably made of ceramic made of aluminum nitride. Flange portions 12 aand 112 a have an outer diameter smaller than that of cylindrical member15. Accordingly, flange portions 12 a and 112 a have an upper surfacecovered with an inner peripheral portion of an end surface of one endportion of cylindrical member 15 on a side facing conductor 11. Hole 10b may have a simple shape having no step in the direction of thethickness of disk-shaped member 10, or, as shown in FIG. 2, hole 10 bmay have a bottom with a stepped portion 10 d in conformity with flangeportions 12 a, 112 a, annular member 14, and member 114 in the form ofthe hollowed conical frustum having an outer diameter smaller than theouter diameter of cylindrical member 15.

Even when stepped portion 10 d is not provided or when stepped portion10 d is provided at the bottom of hole 10 b, flange portions 12 a and112 a have an upper portion slightly protruding from stepped portion 10d. Therefore, a gap G1 is formed between an outer peripheral portion ofthe end surface of one end portion of cylindrical member 15 on the sidefacing conductor 11 and the bottom of hole 10 b or stepped portion 10 dfacing the outer peripheral portion. Further, a gap G2 is formed betweenan outer peripheral surface of the one end portion of cylindrical member15 and an inner wall of hole 10 b facing the outer peripheral surface.Further, a gap G3 is formed between an inner peripheral surface of theone end portion of cylindrical member 15 and an outer peripheral surfaceof electrode terminal portion 12, 112 facing the inner peripheralsurface. A sealing member 16 suitably made of a glass material isintroduced to fill these gaps G1 to G3.

Cylindrical member 15, at the other end portion thereof facing away fromthe one end portion thereof facing conductor 11, has a diameter-reducedportion 15 a having an outer peripheral surface with a reduced diameterand a diameter-increased portion 15 b having an inner peripheral surfacewith an increased diameter, as shown in FIG. 5. From another point ofview, cylindrical member 15 has a first end portion 151 fitted outsidecolumnar portion 12 c, 112 d and facing conductor 11 and a second endportion 152 facing away from first end portion 151, second end portion152's outer diameter being smaller than first end portion 151's outerdiameter, second end portion 152's inner diameter being larger thanfirst end portion 151's inner diameter. Thus, when cylindrical member 15is fitted outside electrode terminal portion 12, an outer annular spaceS1 is formed between diameter-reduced portion 15 a and an inner wall ofhole 10 b facing diameter-reduced portion 15 a. Further, an innerannular space S2 is formed between diameter-increased portion 15 b andan outer peripheral surface of electrode terminal portion 12, 112 facingdiameter-increased portion 15 b.

When sealing member 16 is used for sealing, glass heated and thusfluidized (or fused) can be pressed by cylindrical member 15 fittedoutside electrode terminal portions 12 and 112 to satisfactorily fillgaps G1 to G3, for example, as will be described hereinafter. In doingso, pressing the glass until sealing member 16 protrudes from gaps G2and G3 ensures that sealing member 16 spreads throughout gaps G1 to G3.Gap G2 is immediately adjacent to outer annular space S1. Gap G3 isimmediately adjacent to outer annular space S2. Accordingly, sealingmember 16 protruding from gap G2 and gap G3 is accommodated in outerannular space S1 and inner annular space S2. This can prevent sealingmember 16 from protruding on a surface of disk-shaped member 10. Thus,such a problem as poor attachment is less likely to occur.

Further, causing sealing member 16 to protrude into outer annular spaceS1 and inner annular space S2 that are larger than gap G2 and gap G3ensures that it can be visually confirmed that sealing member 16 hasfilled gaps G1 to G3 without a substantial gap. Thus, highly reliableshowerhead 4 which is less likely to cause poor connection at anelectrical connection portion between conductor 11 for an upperelectrode and electrode terminal portion 12 for feeding the conductorwith power even when the showerhead is used for a long time in acorrosive environment, can be manufactured without variation.

Hereinafter, a specific example of a method for manufacturing ashowerhead will be described for showerhead 4 including disk-shapedmember 10 having the sealing structure shown in FIG. 3A as arepresentative. A case where disk-shaped member 10 is composed of aceramic material which is aluminum nitride will be described by way ofexample. Initially, 0.5 parts by mass of yttrium oxide as a sinteringaid is added to 99.5 parts by mass of aluminum nitride powder and abinder and an organic solvent are further added thereto, and a ball millis used to mix them together to prepare slurry. The slurry is sprayed ina spray dry method to prepare granules which are in turn press-formed toprepare two formed bodies. The formed bodies are degreased at 700° C. ina nitrogen atmosphere and then sintered at 1850° C. in a nitrogenatmosphere to provide two sintered aluminum nitride bodies.

These two sintered aluminum nitride bodies are each processed into theform of a disk of a prescribed size and subsequently, in order to formconductor 11, a W (tungsten) paste is applied to one side of one of thealuminum nitride bodies by screen-printing, and subsequently, degreasingis performed in a nitrogen atmosphere at 700° C. and thereafter firingis performed in a nitrogen atmosphere at 1830° C. An adhesive materialcontaining aluminum nitride as a main component for adhesion is appliedto one side of the other sintered body and subsequently, degreasing isperformed. These two sintered aluminum nitride bodies are joined andthus bonded such that conductor 11 is inside.

The thus formed, disk-shaped bonded body is machined or the like andthus perforated to have a plurality of gas discharging holes 10 a havinga predetermined inner diameter and arranged in a pattern as shown inFIG. 1 for example. Subsequently, hole 10 b reaching conductor 11 isformed in the peripheral portion. Electrode terminal portion 12 made ofW (tungsten) having flange portion 12 a at an end portion thereof on aside of connection with conductor 11 is connected via connection portion20 to conductor 11 partially exposed from the bottom of hole 10 b.Connection portion 20 includes annular member 14 made of W (tungsten)and plate-shaped member 13. Connection portion 20 can be formed byfitting a previously annularly formed W (tungsten) member (annularmember 14) to an outer peripheral surface of plate-shaped member 13.Thus, electrode terminal portion 12 is electrically connected toconductor 11 via annular conductive portion 14.

Subsequently, a glass preform formed in a doughnut shape for sealing isinserted in hole 1 b at a bottom thereof around a portion at whichelectrode terminal portion 12 is connected. Then, cylindrical member 15made of aluminum nitride as shown in FIG. 5 is fitted outside electrodeterminal portion 12. In doing so, cylindrical member 15 is disposed sothat an end portion thereof facing away from a side thereof having anouter peripheral surface with diameter-reduced portion 15 a and an innerperipheral surface with diameter-increased portion 15 b faces conductor11. Subsequently, the above glass preform is fused, and until the fusedglass protrudes into outer annular space S1 between diameter-reducedportion 15 a and the inner wall surface of hole 10 b facingdiameter-reduced portion 15 a and inner annular space S2 betweendiameter-increased portion 15 b and the outer peripheral surface ofelectrode terminal portion 12 facing diameter-increased portion 15 b,cylindrical member 15 is pressed toward conductor 11 to introducesealing member 16. After the sealing member is introduced, it is left tobe cooled and thus solidified. A showerhead can thus be manufactured.

It should be understood that the embodiments disclosed herein have beendescribed for the purpose of illustration only and in a non-restrictivemanner in any respect. The scope of the present invention is defined bythe terms of the claims, rather than the description above, and isintended to include any modifications within the meaning and scopeequivalent to the terms of the claims.

REFERENCE SIGNS LIST

1: semiconductor manufacturing apparatus

2: semiconductor wafer

3: chamber

4: showerhead

8: wafer holder

9: wafer carrying surface

10: disk-shaped member

10 a: gas discharging hole

10 b: hole

10 c: female screw portion

10 d: stepped portion

11: conductor

12, 112: electrode terminal portion

12 a, 112 a: flange portion

12 b, 112 b: base portion

12 c, 112 c: columnar portion

13: plate-shaped member

14: annular member

15: cylindrical member

151: first end portion

152: second end portion

15 a: diameter-reduced portion

15 b: diameter-increased portion

16: sealing member

20, 200: connection portion

112 b: male screw portion

113: truncated conical member

114: member in the form of a hollowed conical frustum

G1, G2, G3: gap

S1: outer annular space

S2: inner annular space

The invention claimed is:
 1. A showerhead provided in a chamber of asemiconductor manufacturing apparatus and facing a wafer holder,comprising: a disk-shaped member having a plurality of through holespenetrating the disk-shaped member in a direction of a thicknessthereof; a high-frequency conductor embedded in the disk-shaped member;a hole provided in the disk-shaped member, extending in the direction ofthe thickness of the disk-shaped member and having a bottom exposing aportion of the conductor; an electrode terminal portion disposed in thehole and having a base portion electrically connected to the conductorand a columnar portion provided on the base portion; a cylindricalmember having a first end portion fitted outside the columnar portionand facing the conductor and a second end portion facing away from thefirst end portion, the second end portion's outer diameter being smallerthan the first end portion's outer diameter, the second end portion'sinner diameter being larger than the first end portion's inner diameter;and a sealing member surrounding the first end portion.
 2. Theshowerhead according to claim 1, further comprising a connection portion(Applicant's 20; FIG. 3A) that is disposed in the hole and electricallyconnects the conductor and the base portion.
 3. The showerhead accordingto claim 1, wherein the base portion has a flange portion facing theconductor.
 4. The showerhead according to claim 3, wherein thecylindrical member covers at least a portion of an upper surface of theflange portion by the first end portion.
 5. The showerhead according toclaim 2, wherein the connection portion includes a conductive annularmember.
 6. The showerhead according to claim 2, wherein the connectionportion includes a conductive member in a form of a hollowed conicalfrustum increased in diameter in a direction from the conductor towardthe base portion.
 7. The showerhead according to claim 1, wherein thesealing member fills a gap formed between the cylindrical member and theelectrode terminal portion and a gap formed between the cylindricalmember and the hole.
 8. The showerhead according to claim 1, wherein thecylindrical member is made of aluminum nitride, and the sealing memberis made of glass.
 9. A method for manufacturing a showerhead,comprising: forming a hole in a disk-shaped member, which has ahigh-frequency conductor embedded therein, in a direction of a thicknessof the disk-shaped member to expose a portion of the conductor;connecting an electrode terminal portion to the conductor exposed at abottom of the hole; fitting a glass preform in a form of a doughnut tothe electrode terminal portion; fitting to the electrode terminalportion a cylindrical member having a first end portion facing theconductor and a second end portion facing away from the first endportion, the second end portion's outer diameter being smaller than thefirst end portion's outer diameter, the second end portion's innerdiameter being larger than the first end portion's inner diameter;fusing the glass preform; pressing the cylindrical member toward theconductor until the fused glass preform protrudes into a gap between thesecond end portion's outer diameter and an inner wall of the hole and agap between the diameter-increased portion and an outer peripheralsurface of the electrode terminal portion; and solidifying the fusedglass preform to seal the cylindrical member.